1. Field of the Invention
The present invention relates to a fuse structure, and in particular fuse structure that can avoid damage from the laser blow process in its laser spot.
2. Description of the Related Art
Fuses are routinely used in the design of monolithic integrated circuits (IC). Fuses are programming elements for the product after monolithic integrated circuit manufacture programming.
It is well known that random access memories (RAM) are designed with redundancies which include spare columns, rows, or even fully functional arrays, wherein when any element fails, the defective row, column and the like are replaced by a corresponding element. Disabling and enabling of spare elements is accomplished by fuses which are blown when required, preferably, by a laser beam.
Additionally, the technique of laser fuse deleting (trimming) has been widely used both in the memory and logic IC fabrication industries, as an effective way to improve functional yields and to reduce development cycle time. Yet, fuse blow yield and fuse reliability have been problematic in most conventional fuse designs.
FIG. 1 is a sectional view of a traditional fuse structure, FIG. 2 is a top view of a traditional fuse structure, and FIG. 1 shows a cross section C-Cxe2x80x2 of FIG. 2.
Referring to FIG. 1, symbol 100 shows a substrate having a laser spot 110. A metal layer M0 is formed on part of the substrate 100. A metal layer M1 is formed on part of the oxide layer, between the metal layer M0 and metal layer M1 having a oxide layer 120. A conductive plug 130 penetrating the oxide layer 120 electrically connects the metal M0 layer and M1 layer. A laser spot 110 on part of the metal M1 layer and the top of a part of the oxide layer 120 forms a fuse window 140. The symbol 150 is a passivation layer.
Referring to FIG. 2 is a top view of FIG. 1. There are plural fuse structures 210, 220, 230, 240 in fuse window 140. Each fuse structure comprises the M0 layer, the conductive plug 130 and the M1 layer. The solid line area shows the M1 layer, the dashed line area shows M0 layer, and each fuse structure comprises its own optimal laser spot 11. To give an example, a laser beam 290 blows the position 110 of the fuse structure 220. Because of misalignment of the laser beam 290 or thermal scattering of the laser beam 290, thermal shock from the laser blow process can damage the M0 layer. This can cause the fuse structures to crack, seriously affecting device reliability and yield.
Accordingly, an object of the invention provides a fuse structure comprising a substrate, a plurality of conductive layers, a dielectric layer and a plurality of conductive plugs in a new arrangement, increasing the distance between different fuse units.
Another object of the invention provides a fuse window having a plurality of fuse structures, each of the fuse structures comprising a substrate, a plurality of conductive layers, a dielectric layer and a plurality of conductive plugs. The fuse units do not electrically connect to each other.